Radio receiver ignition interference tester



March 7, 1950 RADIO RECEIVER IGNITION INT-ERFERENCE TESTER Filed Jan.' 17, 1946 Patented Mar. 7, 1950 RADIO RECEIVER IGNITION INTERFERENCE TESTER Warren D. Nupp, Drexel Hill, Pa.

` Application January 17, 1946,

3 Claims.

amended April 30,

This invention relates electrical apparatus for from ignition systems.

The use of tuned receivers for locating and measuring radio noise from the ignition system of aircraft engines has required a multiplicity of test equipment and experienced personnel for its operation, largely due to the extensive freluency spectrum involved. My invention has the advantages of being simple, it eliminates the usual tuned circuits, and obtains as wide a frequency response as possible. It combines sufficient sensitivity with simplicity, thereby having considerable utility for use by inexperienced personnel involved in detecting and eliminating radio noise from ignition systems.

The figure of the drawing is a wiring diagram disclosing my invention.

Numeral I consists of a three-inch electrostatically shielded, loop antenna probe for magnetic R. F. pick-up. It is connected to an untuned grid-leak detector 2 and audio lter 3 by means of coaxial cable 4. Audio amplifier 5 is connected between headphones 6 and detector 2. Said headphones are used for monitoring the output. Use of the loop probe necessitated the audio filter 3 preceding the detector 2 to eliminate the sginal produced by the audio frequency magnetic eld about a magneto, since this field produces a very strong signal regardless of the condition of radio shielding provided by a magneto housing. Although the audio lter 3 removes this signal conductively, the detector 2 must be kept at least three feet from a magneto to prevent direct pick-up unless the detector is provided with magnetic shielding in addition to radio shielding. The coaxial cable from the loop to the detector must be short to obtain best sensitivity. Four and one-half feet of coaxial cable have been used with good results.

The B-voltage supply 9 can be any conventional source of continuing voltage, such as a battery, adequate to give the high voltage demanded by the plate 'I of detector 2.

The A-voltage supply, which supplies the lament 8 of detector 2, can be any conventional source of direct current power supply, such as a battery or rectied commercial voltage, adequate to give the voltage demanded by the lament 8. Direct current is preferred because it removes alternating current hum encountered in.

to an improvement in detecting radio noise Serial No. 641,854

(Cl. Z50-20) (Granted under the act of March 3, 1883, as

the normal operation from a volt 60-cycle line.

The plate 1 cathode In circuit is connected across B-voltage supply 9 through load resistors Il and I2. By-pass condenser I3 is connected across said B-voltage supply. Plate I is connected to one of the input terminals I4 of ampliiier 5 through coupling capacitor I5. The other terminal I6 of amplifier 5 is connected to the negative side of said B-voltage suppl Control grid I1 is connected to audio filter output terminal I8 through grid capacitor I9; audio lter output terminal 20 is electrically connected to the negative side of B-voltage supply. Gridleak resistor 2I is connected between said control grid I'I and negative side of said B-voltage supply 9.

Suppressor grid 22 is connected to the cathode I0; screen grid 23 is connected to the cathode return through capacitor 221, and to the plate circuit intermediate resistors II and I2, through resistor 25. Capacitor 2B is connected between plate 'I and cathode I0.

Operation The loop antenna probe I is moved about and over a magneto or other portion of an ignition system in search of a source of radio noise. Radio frequency noise energy emanated by said magneto is picked up by the loop antenna probe. From the loop antenna the picked up energy is fed into the audio lter 3, throughcoaxial cable 4. Said filter eliminates the signal produced by the strong audio frequency magnetic eld about a magneto. The radio frequency output is then fed into grid-leak detector 2 which changes the alternating high frequency noise signal voltages into pulsating current, and other- Wise amplies. The pulsating current output is amplied 5 and fed into the headphone Where the electric pulsations are converted into sound energy. No tuning is necessary as the circuit is untuned and responds to a wide range of frequencies. A sound heard in the headphones is an indication that the probe is over a radio noiseemitting source. Measures can then be taken to shield or otherwise eliminate the disturbance at such source. f

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto, since many modiiications may be made by those skilled in the art.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

What is claimed is:

1. An ignition interference tester, comprising: an electro-statically shielded loop antenna probe; an audio lter; a coaxial cable connecting said probe and said lter; an audio amplier; an untuned grid-leak detector connected between said lter and said amplifier; and a headphone connected across the output of said ampliiier.

2. An ignition interference tester, comprising:

an electro-statically shielded loop antenna probe;

an audio iilter connected to the output of said antenna; a headphone; and an untuned magnetically and radio shielded detector connected across the output and input terminals of said filter and said headphone, respectively.

3. An ignition interference tester, comprising: an electro-statically shielded loop antenna probe pick-up; an audio lter of a non-dissipating type, a low-loss transmission line connecting said probe and said filter; a high gain audio amplier; an untuned grid-leak detector connected between said lter and said amplifier; and a headphone connected across the output of said ampliler.

WARREN D. NUPP.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,606,283 Wolf Nov. 9, 1926 1,757,333 Ranger May 6, 1930 1,811,357 Karplus June 23, 1931 2,064,469 Haeff Dec. 15, 1936 2,192,321 Meier Mar. 5, 1940 

